In the proposed studies, we seek to refine further the I125 antiglobulin technique for quantitating erythrocyte coating with IgG, C4 and C3. We plan also to develop the inhibition technique for Borsos and Leonard for quantitating these substances. We will compare the efficacy and adaptability of each of these techniques to quantitating IgG, C4 and C3 on red cells, in erythrocyte eluates and possibly also on platelets and white cells. In collaborative studies we will see whether these techniques can be used to demonstrate cytotoxic erythroblastic antibodies in patients with pure red cell aplasia. In paroxysmal nocturnal hemoglobinuria, we plan to study mechanisms of hemolysis of PNH and artificial "PNH-like" erythrocytes in the acid hemolysis and sucrose hemolysis reactions. If suitable techniques can be developed we plan to investigate the "hemolysis" of PNH platelets and white cells in these hemolytic systems. In auto-immune hemolytic anemia, we plan to correlate hemolytic rates with quantitative studies of erythrocyte coating including patients with apparent immune hemolysis but no detectable erythrocyte coating by conventional antibglobulin testing. In other studies we plan to study mechanisms of erythrocyte complement coating in AIHA. We plan also to apply the quantitative techniques developed to certain practical problems in blood banking and immunohematology. In particular, we plan to perform quantitative studies of erythrocyte antibody eluate methods, to study methods of collecting specimens for serologic studies, to explore the use of frozen reagent cells which can be applied to quality control methods for standard antiglobulin testing and quantitative studies of erythrocyte coating.